This invention relates to a flow control device which can control the flow rate of fluid over a wide flow rate range.
Most popular conventional means for feeding fluid through pipes while controlling its flow rate are pumps.
But pumps have a narrow controllable flow rate range. Even gear pumps, which have the widest controllable flow rate range, have a discharge ratio (ratio of the minimum controllable flow rate to the maximum controllable flow rate) of only about 1:10. In fields or applications where the flow rate has to be controlled with higher accuracy over a wider range, pumps are useless.
On the other hand, in the field where textile products are dyed, to cope with a large variety of designs, it is necessary to feed dye solutions that differ widely in concentration from one another into tanks while adjusting the flow rates of the dye solutions with high accuracy. This was usually done by a batch process in which different kinds of powder dyes were weighed out, mixed together and melted to adjust the concentration of each dye solution, and filled in each tank. But in the batch process, the greater the number of kinds of dyes of different concentrations, the more time-consuming it was to prepare dye solutions. It was therefore desired to shorten the time for preparing dye solutions.
It is therefore required to develop an automatic system for preparing dye solutions which can prepare a plurality of kinds of dye solutions having vastly different concentrations from each other with high accuracy and to feed them. Since the discharge ratio controllable by a single pump is 1:10 at the most, one way to construct a system which can cope with such a wide concentration range is to use a plurality of such pumps each for one of a plurality of concentration regions from high to low. Unexamined Japanese patent publication 63-35873 discloses such a structure. But this arrangement needs as many pumps as the number of dye concentration regions, so that the facility and installation costs increase. Thus, such a system is not suitable for industrial production. Desired is a device which can control the flow rate of fluid with high accuracy over a wide flow rate range with a single pump.
An object of this invention is to provide a flow control device which can control the flow rate with extremely high accuracy over a wide flow rate range with a single pump.